In the prior art opposed piston internal combustion engines, two pistons are slidable in a cylinder in an opposed fashion such that they share the same combustion chamber. Both pistons are connected via a connecting rod to a separate crankshaft in such a manner that the pistons reciprocate within the cylinder to vary the combustion chamber volume according to a predetermined cycle.
U.S. Pat. No. 2,486,185 describes an opposed piston internal combustion engine having two separate cranks geared together with a 2:1 ratio. The cycle described synchronizes the power stroke of the two opposed pistons for very large expansion of the combustion gases. U.S. Pat. No. 3,485,221 describes an opposed piston engine having two pistons which are connected to separate crankshafts turning at the same speed and out of phase by 45.degree. with respect to one another, in which the pistons act as slide valves in a two-stroke engine configuration. The opposed piston engine is said to provide high torque output on the crankshafts. U.S. Pat. No. 4,010,611 describes an opposed piston engine wherein both pistons are connected to separate crankshafts and one piston turns at twice the rotational speed of the other. At the beginning of the compression cycle the two pistons are in phase, and the opposed piston motor allows for a maximum expansion and a complete exhaust of the combustion chamber.
Other patents of the prior art show the use of cams in replacement of the conventional connecting rod and crankshaft assembly, as can be found in French patents 707,677 and 846,990 with addition 51,826, United Kingdom patent 472,746, U.S. Pat. Nos. 1,808,664, 1,796,453, 4,520,765 and 4,974,555.
Although the prior art opposed piston engines allow for a variable volume during the expansion or exhaust phases in such a way that efficiency of the engine can be improved, it is required in the case of a four-cycle engine according to the prior art to provide separate valve means for controlling the intake and exhaust valves. Crankshaft engines are required to work within the confines of the sinusoidal displacement of the opposed pistons. This is not the case with cam engines, but the gain in selectable displacement curves of the pistons are eclipsed by the extensive and expensive mechanics required.
In all motors having a given work output, the indicated power is directly proportional to the volumetric efficiency of the engine. Therefore, it is desirable that the intake valves be as large as possible. Furthermore, a large volumetric efficiency can reduce the losses associated with the intake cycle. It is also desirable to minimize the temperature in the tubing, orifices and intake valves in order to limit the heating of the air/fuel mixture. Unfortunately, in existing four-cycle motors the size of the intake valve is limited and the valve seats operate at temperatures great much larger than the cooling liquid. The exhaust valves also affect the volumetric efficiency. They are generally much smaller than the intake valves. The size of the exhaust valves can be reduced to 50% of that of the intake valves. Still, the choice involves a compromise since the work lost during the exhaust increases when the dimension of the exhaust valves is reduced. Therefore the valves always restrict the volumetric efficiency in addition to dynamically limiting the motor speeds due to their inertia. The only cam engine (U.S. Pat. No. 4,520,765) with a four-cycle operation having a large exhaust port in the cylinder wall requires a scavenging of the burnt gases, hence losing all the advantages of such a port.
It is also desirable to carry out the combustion cycle in a constant volume chamber and or at constant pressure to augment thermal efficiency.
The thermal losses during combustion and expansion also reduce the efficiency of the cycle. The greater part of these losses can be attributed to the loss of heat during combustion.
Losses due to friction also affect the efficiency of the engine and 60% of these losses are produced by the friction of the piston rings.
Also, the energy lost in the exhaust gases can be used to increase the thermal efficiency of this cycle. Furthermore, the construction of conventional engines and cam engines requires many stationary and moving parts. This increases the cost of manufacture and reduces reliability and durability of those engines.
It is an object of the present invention to overcome totally or in part the drawbacks of the prior art engines as mentioned above.